Former Scottish secretary Alistair Carmichael has apologised after a Cabinet Office investigation found his special secretary had leaked a story to The Daily Telegraph.
The inquiry was launched in April after the Telegraph reported on a leaked memo stating that Nicola Sturgeon had told the French ambassador that she wanted David Cameron to be Prime Minister after the election.
The Cabinet Office said it had "searched all relevant official phone records, emails and print logs". In addition, all those who had access to the memo were asked to complete a questionnaire and then subsequently interviewed.
The investigation found that an "official mobile phone" held by Carmichael's former special adviser Euan Roddin "was used to make telephone calls to one of the authors of The Daily Telegraph story".
It said: "Mr Roddin confirmed that he provided a copy of the Scotland Office memo to a Daily Telegraph journalist on 1 April 2015, and discussed the memo with the journalist on a number of occasions.
"He told the investigation team that he acted in what he saw as the public interest and that in his view the public needed to be aware of the position attributed to the First Minister."
According to the Cabinet Office report, Carmichael "confirmed that he had been asked by Mr Roddin for his view of the possibility of sharing the memo with the press. Mr Carmichael agreed that this should occur. He recognises that, as a Secretary of State, he was responsible for his own conduct and that of his Special Adviser. He could and should have stopped the sharing of the memo and accordingly accepts responsibility for what occurred." It said that no one else had any involvement.
Cabinet Secretary Sir Jeremy Heywood ordered an inquiry into how the note, which claimed that Sturgeon told ambassador Sylvie Bermann that she would prefer to see Conservatives remain in power after the general election, got into the public domain.
The Cabinet Office investigation concluded that Carmichael "could and should have stopped the sharing of the memo" and added that he "accepts responsibility for what occurred".
Carmichael, who is now Scotland's only Lib Dem MP after the party lost ten of its 11 seats north of the border, said that, while he had not seen the document before it was published by The Daily Telegraph, he was "aware of its content and agreed that my special adviser should make it public".
He stated: "I should not have agreed this. It was an error of judgment which I regret.
"I accept full responsibility for the publication of the document.
"I have written today to the First Minister and to the French Ambassador to apologise to them both."
Carmichael added: "Had I still been a government minister, I would have considered this to be a matter that required my resignation. I have therefore informed the Cabinet Secretary that I will decline my ministerial severance payment."
Sturgeon, the SNP leader, tweeted that she had received a letter from Carmichael "apologising for leak and accepting that contents of memo not correct".
The Liberal Democrat had already confirmed that the memo, containing an account of a private meeting between Sturgeon and the French ambassador, was written in the Scotland Office.
The note went on to say that Sturgeon said she did not think Labour leader Ed Miliband was ''prime minister material''.
At the time Sturgeon insisted that the contents of the memo were ''100% untrue''.
The leaked document was written by a British civil servant following a conversation with consul-general Pierre-Alain Coffinier regarding a meeting between Sturgeon and Bermann, who was on her first visit to Scotland in February.
In his letter to the Scottish First Minister, Carmichael said: "I wish to inform you that I am taking full responsibility for the publication of that document when I was Secretary of State.
"I accept that its publication was a serious breach of protocol and that the details of that account are not correct."
He added: "I am clear that this was an error of judgment on my part and wish to offer you my sincere apologies for the embarrassment caused to you and the French ambassador."
The Cabinet Office has also confirmed that Roddin will not take his severance pay.